1. Field of the Invention
This invention relates generally to prosthetic implants having stem portions and, more particularly, to prosthetic implants having stem portions subject to issues of stress shielding in implant.
2. Related Art
Total hip arthroplasty (THA) is an extremely successful surgical technique. With the improvements in varying technologies including cross-linked polyethylenes, metal-on-metal, and ceramic bearings appear to minimize long-term issues related to bone loss due to osteolysis. Now the attention is once again focused on bone maintenance particularly due to effects of the presence of an implant within the femur. A composite beam of the femur and implant is created during surgery. This composite beam results in the stresses being shared between the femur and the implant. The bone, then, is exposed to lower stress levels when the implant supports more of the load.
In 1892, Wolff postulated that the bony struts (Trabecular) of the proximal femur were aligned with the principal structure. Huskes in 1992, one hundred years later, has stated that flexible stems do reduce stress shielding in bone remodeling. Sychtez reported in 2001 that the axial stiffness of the femur accounts for approximately 46% of the variance of the loss of bone. This was the most significant factor influencing atrophy. Another major contributor to bone loss is the implant design itself. In addition to the femur and the implant, patient parameters such as physiological loading, activity levels, etc, may contribute to the remodeling of the femur.
There remains a need in the art for a method to establish design parameters for orthopaedic implants by adjusting local stiffness of implant, based upon combined stiffness of implant/bone composite to minimize stress shielding.